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Needle-like supramolecular amphiphilic assembly constructed by the host–guest interaction between calixpyridinium and methotrexate disodium
Tetrahedron Letters xxx (xxxx) xxx
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Needle-like supramolecular amphiphilic assembly constructed by the host–guest interaction between calixpyridinium and methotrexate disodium Kui Wang ⇑, Mi-Ni Wang, Qi-Qi Wang, Yu-Xin Feng, Yue Wu, Si-Yang Xing ⇑, Bo-Lin Zhu ⇑, Ze-Hao Zhang Tianjin Key Laboratory of Structure and Performance for Functional Molecules, MOE Key Laboratory of Inorganic-Organic Hybrid Functional Material Chemistry, College of Chemistry, Tianjin Normal University, Binshuixi Road 393, Xiqing District, Tianjin 300387, China
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Article history: Received 30 September 2019 Revised 28 October 2019 Accepted 2 November 2019 Available online xxxx Keywords: Supramolecular assembly Host–guest systems Macrocycle Calixpyridinium
a b s t r a c t In this work, the host–guest interaction between calixpyridinium and the anionic anticancer drug methotrexate disodium was explored in water. Unexpectedly, an interesting anisotropic needle-like rather than an ordinary isotropic spherical supramolecular amphiphilic assembly was fabricated by the complexation of calixpyridinium with methotrexate disodium. It is the second anionic guest to be discovered to form the non-spherical supramolecular assembly upon complexation with calixpyridinium. This discovery implies the possibility to construct various topological nanostructures based on the host–guest interactions between calixpyridinium and the anionic drugs in the future. The resulting calixpyridinium– drug assemblies with different morphologies may have the diverse potentials to adjust the efficacies of anionic drugs. Ó 2019 Elsevier Ltd. All rights reserved.
Introduction Cancer is one of the diseases with highest morbidity and mortality in the world. According to the world health organization, one in 5 men and one in 6 women worldwide develop cancer during their lifetime, and one in 8 men and one in 11 women die from the disease [1]. Up to now, the etiology of malignant tumor has not been fully understood yet. Although the new therapies appear continuously, cancer has not been completely conquered. Chemotherapy is still one of the most effective antitumor therapies [2,3]. However, most chemotherapeutic agents have serious side effects. They cannot distinguish cancer cells from normal tissue. Therefore, chemotherapy is a double-edged sword and it causes great suffering to patients. Recently, the method of supramolecular inclusion by the macrocyclic hosts paves a smart way to reduce the side effects of drugs. Zhang et al. proposed a new concept of supramolecular chemotherapy, which aimed to reduce the toxicity of chemotherapeutic drugs to normal cells and improve their anti-cancer efficacy by combining the macrocyclic hosts and the anticancer drugs based on host–guest interactions [4]. Some macrocyclic hosts, such as cucurbit[7]uril and water-soluble pillar[6]arene, have been ⇑ Corresponding authors. E-mail addresses: [email protected] (K. Wang), [email protected] (S.-Y. Xing), [email protected] (B.-L. Zhu).
successfully applied in the supramolecular chemotherapy [5–9]. Besides anticancer drugs, the efficacies of other drugs have also been successfully adjusted by the method of supramolecular inclusion based on the macrocyclic cucurbiturils [10–14], cyclodextrins [15], pillararenes [16], and sulfonatocalixarenes [17–19]. It is noticeable, however, most of these frequently used macrocyclic hosts in this field are the suitable receptors for cationic and neutral drugs. Adjusting the efficacies of the anionic drugs by supramolecular strategy based on the inclusion of macrocyclic hosts via the host–guest interactions has been explored much less frequently. In fact, the anionic drugs are also quite widespread and important. Calixpyridinium, obtained by the oligomerization of 3-bromomethylpyridine, is a positively charged macrocyclic host and has excellent water-solubility [20]. In recent years more and more attentions have been paid in this macrocyclic host because it has exhibited good binding abilities with anionic guests in aqueous solution [20–24]. Moreover, polyanionic guests [25–28] and anionic gemini surfactant guests [29] have been found to form the higherorder assemblies rather than the simple complexes upon complexation with calixpyridinium. Although calixpyridinium has been proved to be a good receptor for anions in aqueous media [30], the host–guest interactions between calixpyridinium and the anionic drugs have been explored much less frequently. Recently, we reported a study on the host–guest interaction between calixpyridinium and the anionic anticancer drug Alimta. The isotropic spherical supramolecular amphiphilic assembly rather than the simple
https://doi.org/10.1016/j.tetlet.2019.151357 0040-4039/Ó 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: K. Wang, M. N. Wang, Q. Q. Wang et al., Needle-like supramolecular amphiphilic assembly constructed by the host–guest interaction between calixpyridinium and methotrexate disodium, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.151357
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Scheme 1. Schematic illustration of the needle-like supramolecular assembly constructed by the host–guest interaction between calixpyridinium and MTX.
Fig. 1. Dependence of the optical transmittance at 500 nm on the MTX concentration in the presence of 0.10 mM (a), 0.15 mM (b), and 0.20 mM (c) calixpyridinium.
complex was unexpectedly fabricated benefitting from the additional charge-transfer interactions besides the electrostatic interactions between calixpyridinium and Alimta [31]. Macrocyclic
host-based supramolecular amphiphilic assembly can be tailored to construct various topological nanostructures, and therefore fulfill multiple applications [32–38]. Inspired by this new discovery, we
Please cite this article as: K. Wang, M. N. Wang, Q. Q. Wang et al., Needle-like supramolecular amphiphilic assembly constructed by the host–guest interaction between calixpyridinium and methotrexate disodium, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.151357
K. Wang et al. / Tetrahedron Letters xxx (xxxx) xxx
tried to fabricate more topological nanostructures that were different from ordinary isotropic spheres based on the supramolecular amphiphilic assembly between calixpyridinium and the anionic drugs. Methotrexate disodium (MTX) is a folate antagonist and has been widely used in the treatment of various types of cancers including breast, leukemia, lymphoma, lung and osteosarcoma [39]. Herein, the host–guest interaction between calixpyridinium and MTX was explored. Unexpectedly, completely differing from the ordinary isotropic spherical supramolecular amphiphilic assembly constructed by the host–guest interaction between calixpyridinium and Alimta, an interesting anisotropic needle-like supramolecular assembly was fabricated (Scheme 1), although the structures of Alimta and MTX are very similar. It is the second anionic guest to be discovered to form the non-spherical supramolecular assembly upon complexation with calixpyridinium besides sodium alginate with low viscosity, which formed a lamellar structure by the host– guest interaction of calixpyridinium [25]. This discovery implies the possibility to construct various topological nanostructures based on the host–guest interactions between calixpyridinium and the anionic drugs in the future. The resulting calixpyridinium–drug assemblies with different morphologies may have the diverse potentials to adjust the efficacies of the anionic drugs. Results and discussion The calixpyridinium-complexation-induced critical aggregation concentration (CAC) of MTX was first determined by measuring the optical transmittance of the calixpyridinium solution in the presence of different concentrations of MTX (Fig. S1). As can be seen from Fig. 1, there was no obvious change in the optical
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transmittance of the calixpyridinium solution over 500 nm with the addition of a small amount of MTX. Further addition of MTX leaded to a dramatic decrease in the optical transmittance of the calixpyridinium solution over 500 nm accompanied by the appearance of turbidity because of the supramolecular amphiphilic assembly between calixpyridinium and MTX. The calixpyridinium-complexation-induced CAC of MTX could therefore be determined by observing the inflection point on the plot of the optical transmittance at 500 nm versus the concentrations of MTX: 120 lM at 0.10 mM calixpyridinium, 100 lM at 0.15 mM calixpyridinium, and 53 lM at 0.20 mM calixpyridinium. The calixpyridinium-complexation-induced CAC of MTX was further determined by measuring the electrical conductivity of the calixpyridinium solution in the presence of different concentrations of MTX. As can be seen from Fig. 2, the addition of a small amount of MTX leaded to a linear increase in the electrical conductivity of the calixpyridinium solution. Further addition of MTX leaded to a slower increase in the electrical conductivity of the calixpyridinium solution because of the formation of large calixpyridinium–MTX supramolecular amphiphilic assembly. The calixpyridinium-complexation-induced CAC of MTX could therefore be determined by observing the inflection point on the plot of the electrical conductivity versus the concentrations of MTX: 40 lM at 0.10 mM calixpyridinium, 70 lM at 0.15 mM calixpyridinium, and 37 lM at 0.20 mM calixpyridinium. The calixpyridinium-complexation-induced CAC values of MTX determined by optical transmittance and electrical conductivity were in the same order of magnitude. Next, the MTX-complexation-induced CAC of calixpyridinium was determined by measuring the optical transmittance of the
Fig. 2. Dependence of the electrical conductivity on the MTX concentration in the presence of 0.10 mM (a), 0.15 mM (b), and 0.20 mM (c) calixpyridinium in water.
Please cite this article as: K. Wang, M. N. Wang, Q. Q. Wang et al., Needle-like supramolecular amphiphilic assembly constructed by the host–guest interaction between calixpyridinium and methotrexate disodium, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.151357
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Fig. 3. Dependence of the optical transmittance at 500 nm on the calixpyridinium concentration in the presence of 0.07 mM (a), 0.10 mM (b), and 0.15 mM (c) MTX.
MTX solution in the presence of different concentrations of calixpyridinium (Fig. S2). As can be seen from Fig. 3, similarly, there was no obvious change in the optical transmittance of the MTX solution over 500 nm with the addition of a small amount of calixpyridinium. Further addition of calixpyridinium leaded to a dramatic decrease in the optical transmittance of the MTX solution over 500 nm accompanied by the appearance of turbidity because of the supramolecular amphiphilic assembly between calixpyridinium and MTX. The MTX-complexation-induced CAC of calixpyridinium could therefore be determined by observing the inflection point on the plot of the optical transmittance at 500 nm versus the concentrations of calixpyridinium: 29 lM at 0.07 mM MTX, 72 lM at 0.10 mM MTX, and 8.6 lM at 0.15 mM MTX. The MTX-complexation-induced CAC of calixpyridinium was also further determined by measuring the electrical conductivity of the MTX solution in the presence of different concentrations of calixpyridinium. As can be seen from Fig. 4, similarly, the addition of a small amount of calixpyridinium leaded to a linear increase in the electrical conductivity of the MTX solution. Further addition of calixpyridinium leaded to a slower increase in the electrical conductivity of the MTX solution because of the formation of calixpyridinium–MTX supramolecular amphiphilic assembly. The MTXcomplexation-induced CAC of calixpyridinium could therefore be determined by observing the inflection point on the plot of the electrical conductivity versus the concentrations of calixpyridinium: 98 lM at 0.07 mM MTX, 168 lM at 0.10 mM MTX, and 4.4 lM at 0.15 mM MTX. The MTX-complexation-induced CAC values of calixpyridinium determined by optical transmittance and electrical conductivity were also in the same order of magnitude. Although different concentrations of calixpyridinium and MTX can all mutually induce aggregation, it is necessary to determine
the optimal stoichiometry between calixpyridinium and MTX for constructing the calixpyridinium–MTX supramolecular amphiphilic aggregates via the continuous variation method by observing the dependence of the optical transmittance at 500 nm on the molar ratio of calixpyridinium (Fig. S3). As can be seen from Fig. 5, a minimum was determined in the Job’s plot for a 0.33 M ratio of calixpyridinium when the total concentration of calixpyridinium and MTX was kept constant at 0.20 mM. This indicated that the optimal stoichiometry between calixpyridinium and MTX for constructing the calixpyridinium–MTX supramolecular aggregates is 1:2. It was also a charge matching ratio between calixpyridinium and MTX. The CAC of the 1:2 calixpyridinium–MTX complex for constructing the supramolecular aggregates was further determined by measuring the optical transmittance of different concentrations of the 1:2 calixpyridinium–MTX solution (Fig. S4). As can be seen from Fig. 6, there was no obvious change in the optical transmittance over 500 nm with the addition of a small amount of the 1:2 calixpyridinium–MTX complex. Further addition of the 1:2 calixpyridinium–MTX complex leaded to a dramatic decrease in the optical transmittance over 500 nm accompanied by the appearance of turbidity because of the supramolecular amphiphilic assembly between calixpyridinium and MTX. The CAC of the 1:2 calixpyridinium–MTX complex for constructing the supramolecular aggregates could therefore be determined by observing the inflection point on the plot of the optical transmittance at 500 nm versus the concentrations of calixpyridinium: 42 lM calixpyridinium–84 lM MTX. Further studies on the calixpyridinium– MTX aggregates were focused on a concentration of 0.10 mM calixpyridinium–0.20 mM MTX. This concentration is far higher than its CAC to ensure the complete aggregation between calixpyridinium and MTX.
Please cite this article as: K. Wang, M. N. Wang, Q. Q. Wang et al., Needle-like supramolecular amphiphilic assembly constructed by the host–guest interaction between calixpyridinium and methotrexate disodium, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.151357
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Fig. 4. Dependence of the electrical conductivity on the calixpyridinium concentration in the presence of 0.07 mM (a), 0.10 mM (b), and 0.15 mM (c) MTX in water.
Fig. 5. Job’s plot for calixpyridinium and MTX in water. [Calixpyridinium] + [MTX] = 0.20 mM.
As can be seen from Fig. 7a, the calixpyridinium–MTX solution showed the obvious Tyndall effect because of the existence of abundant nanoparticles formed by the supramolecular amphiphilic assembly between calixpyridinium and MTX. However, no Tyndall effect was observed for free calixpyridinium and MTX solutions, proving that free calixpyridinium and MTX could not form aggregates under the same conditions. Furthermore, 1-methylpyridinium, the building subunit of calixpyridinium, could also not form supramolecular aggregates upon complexation with MTX, which has been proved by the Tyndall effect (Fig. 7a) and the
Fig. 6. Dependence of the optical transmittance at 500 nm on the calixpyridinium concentration in the calixpyridinium–MTX solution with a fixed 1:2 stoichiometry.
optical transmittance (Fig. 7b). This implied that the cyclic polycationic structure of calixpyridinium was a crucial factor for the supramolecular amphiphilic assembly between calixpyridinium and MTX. High-resolution transmission electron microscopy (TEM), scanning electron microscope (SEM) and dynamic light scattering (DLS) were then employed to determine the structure and size of the calixpyridinium–MTX supramolecular aggregates. Unexpectedly, completely differing from the ordinary spherical supramolecular aggregates formed by the complexation of calixpyridinium with Alimta [31], an interesting needle-like supramolecular amphiphilic assembly was constructed
Please cite this article as: K. Wang, M. N. Wang, Q. Q. Wang et al., Needle-like supramolecular amphiphilic assembly constructed by the host–guest interaction between calixpyridinium and methotrexate disodium, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.151357
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Fig. 7. (a) Photograph showing the Tyndall effect of 1-methylpyridinium chloride + MTX (I), free MTX (II), free calixpyridinium (III) and calixpyridinium + MTX (IV). (b) Optical transmittance of calixpyridinium, MTX, calixpyridinium + MTX, and 1-methylpyridinium chloride + MTX in water. (c) High-resolution TEM image of the calixpyridinium–MTX assemblies. (d) SEM image of the calixpyridinium–MTX assemblies. (e) DLS data of the calixpyridinium–MTX assemblies. [Calixpyridinium] = 0.10 mM, [MTX] = 0.20 mM, and [1-methylpyridinium chloride] = 0.40 mM.
(Figs. 7c, d and S5), although the structures of Alimta and MTX are very similar. The average diameter of the supramolecular amphiphilic aggregates in solution measured by DLS was 532.7 nm (Fig. 7e). The binding mode of calixpyridinium with MTX in the calixpyridinium–MTX supramolecular aggregates was further deduced by analyzing complexation-induced 1H chemical shift changes (Dd) of calixpyridinium and MTX. As shown in Fig. 8, an obvious upfield shift was found for the Hb, Hc, Hd, and He proton signal of calixpyridinium upon complexation with MTX. Meanwhile, an obvious downfield shift was found for the Ha proton signal of calixpyridinium. This indicated undoubtedly that MTX was bound with calixpyridinium. Compared with the binding structure between
calixpyridinium and Alimta in the calixpyridinium–Alimta supramolecular aggregates, MTX was bound much closer to the cavity of calixpyridinium because the Ha proton signal of calixpyridinium almost did not shift upon complexation with Alimta [31]. It may be a key factor for the different morphologies formed by the complexation of calixpyridinium with MTX and Alimta as shown in Scheme 1. On the other hand, as shown in Fig. 8, an obvious upfield shift was found for the H1–H4 proton signal of MTX upon complexation with calixpyridinium while the H6 proton signal of MTX almost did not shift, which implied that the nitrogen heterocyclic ring and benzene ring were two possible charge-transfer binding sites of MTX with calixpyridinium. The color of the MTX solution became darker upon complexation with calixpyridinium
Please cite this article as: K. Wang, M. N. Wang, Q. Q. Wang et al., Needle-like supramolecular amphiphilic assembly constructed by the host–guest interaction between calixpyridinium and methotrexate disodium, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.151357
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Fig. 8. 1H NMR spectra of calixpyridinium (bottom), MTX (top), and calixpyridinium–MTX complex (middle) in D2O solutions. Inset: the color of the D2O solution of calixpyridinium (bottom), MTX (top), and calixpyridinium–MTX complex (middle). [Calixpyridinium] = 5 mM, and [MTX] = 10 mM.
Fig. 9. (a) Dependence of the optical transmittance at 500 nm of the calixpyridinium–MTX assembly on time within 18 h at room temperature in water. (b) Optical transmittance of the calixpyridinium–MTX assembly before and after centrifugation for one minute at 1000 r/min in aqueous solution. Inset: the Tyndall effect of the calixpyridinium–MTX solution before (I) and after centrifugation for one minute (II). [Calixpyridinium] = 0.10 mM, and [MTX] = 0.20 mM.
(Fig. 8), which further proved the existence of a charge-transfer interaction between calixpyridinium and MTX. Meanwhile an obvious downfield shift was found for the H7 proton signal of MTX while the H5 and H8 proton signal of MTX almost did not shift, which implied that the negatively charged carboxylate connected to H7 was the third possible binding site of MTX with calixpyridinium accompanied by electrostatic interactions. The binding ability of calixpyridinium with MTX was further estimated by the competitive binding of MTX with calixpyridinium. As can be seen from Fig. S6a, the addition of 2 equiv of MTX in the calixpyridinium–1,3,6,8-pyrenetetrasulfonic acid tetrasodium salt (PyTS) solution could not affect its optical transmittance, suggesting that MTX could not competitively bind with the calixpyridinium in calixpyridinium–PyTS complex. However, as can be seen from Fig. S6b, the addition of 2 equiv of MTX in the calixpyridinium–glyphosate solution leaded to a decrease in
its optical transmittance, suggesting that MTX could competitively bind with the calixpyridinium in calixpyridinium–glyphosate complex to form calixpyridinium–MTX aggregates. Both of the two competitive binding experimental results indicate that the binding ability of calixpyridinium with MTX is moderate because the binding ability of calixpyridinium with PyTS and glyphosate is strong (The binding constant is in the order of magnitude of 106 M 1) [23] and weak (The binding constant is in the order of magnitude of 102 M 1) [24], respectively. In order to explore the stability of the calixpyridinium–MTX supramolecular aggregates, their tolerance to time, centrifugation, temperature and even salt was studied. As can be seen from Figs. S7 and 9a, there was no obvious change in the optical transmittance of the calixpyridinium–MTX solution over at least 18 h at room temperature. The optical transmittance and the Tyndall effect of the calixpyridinium–MTX solution could also not be
Please cite this article as: K. Wang, M. N. Wang, Q. Q. Wang et al., Needle-like supramolecular amphiphilic assembly constructed by the host–guest interaction between calixpyridinium and methotrexate disodium, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.151357
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Fig. 10. (a) Dependence of the optical transmittance at 500 nm of the calixpyridinium–MTX assembly on the concentration of NaCl. Inset: the Tyndall effect of the calixpyridinium–MTX solution in the absence (I) and presence (II) of 0.54 mM NaCl. (b) Dependence of the optical transmittance at 500 nm of the calixpyridinium–MTX assembly on time within 6 h in the presence of 0.54 mM NaCl. Inset: the Tyndall effect of the calixpyridinium–MTX assembly immediately after the preparation (I) and 6 h after the preparation (II) in the presence of 0.54 mM NaCl. [Calixpyridinium] = 0.10 mM, and [MTX] = 0.20 mM.
Fig. 11. Dependence of the optical transmittance at 500 nm on the MTX concentration in the presence of 0.10 mM calixpyridinium in saline solution.
disturbed after centrifugation for one minute at 1000 r/min (Fig. 9b). Both experimental results indicated that the calixpyridinium–MTX supramolecular aggregates had sufficient stability at room temperature. As can be seen from Fig. S8, there was also no obvious change in the optical transmittance of the calixpyridinium–MTX solution with temperature ascending from 20 to 40 °C, implying that the calixpyridinium–MTX supramolecular aggregates even had sufficient stability to the temperature of a cancer patient with fever. The tolerance of the calixpyridinium– MTX supramolecular aggregates to NaCl was further studied for their possible biomedical applications in a complex biological environment. As can be seen from Figs. S9 and 10a, there was no obvious change in the optical transmittance of the calixpyridinium– MTX solution in the presence of NaCl from 15 lM to 5.34 mM. The Tyndall effect of the calixpyridinium–MTX solution could also not be disturbed in the presence of NaCl (Fig. 10a). Moreover, the optical transmittance and the Tyndall effect of the calixpyridinium–MTX solution in the presence of NaCl could even not be disturbed over 6 h (Figs. S10 and 10b). The calixpyridinium-complexation-induced CAC of MTX was further measured in saline solution (Fig. S11). As can be seen from Fig. 11, the calixpyridinium-complexation-induced CAC of MTX in saline solution was 62 lM at 0.10 mM calixpyridinium, which was in the same order of magnitude as that in pure water. Moreover, the calixpyridinium–MTX supramolecular aggregates in saline solution also
Fig. 12. Dependence of the optical transmittance at 700 nm on the pH value of the calixpyridinium–MTX aqueous solution. Inset: the left photograph showing the Tyndall effect of the calixpyridinium–MTX solution at pH = 6 and pH = 2 at room temperature in water. The right photograph showing the Tyndall effect of the calixpyridinium–MTX solution at pH = 6 and pH = 9 at room temperature in water. [Calixpyridinium] = 0.10 mM, and [MTX] = 0.20 mM.
had sufficient stability (Fig. S12). All of these experimental results in the presence of NaCl suggested that these aggregates were possibly suitable for the biomedical applications. The heat effect for the formation of calixpyridinium–MTX supramolecular amphiphilic aggregates was studied by observing the optical transmittance of the calixpyridinium–MTX solution with a further increase of the temperature. As can be seen from Fig. S13, there was a little increase in the optical transmittance of the calixpyridinium–MTX solution with the temperature ascending from 20 to 60 °C, accompanied by the obvious reduction of the Tyndall effect. This implied that the formation of the calixpyridinium–MTX supramolecular aggregates was exothermic because increasing temperature leaded to the disassembly of the aggregates. The optimal pH environment for the formation of the calixpyridinium–MTX supramolecular aggregates was also studied by observing the optical transmittance of the calixpyridinium–MTX solution at various pH values because both calixpyridinium and MTX could be affected by pH (Fig. S14). As can be seen from Fig. 12, there was an obvious decrease in the optical transmittance
Please cite this article as: K. Wang, M. N. Wang, Q. Q. Wang et al., Needle-like supramolecular amphiphilic assembly constructed by the host–guest interaction between calixpyridinium and methotrexate disodium, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.151357
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of the calixpyridinium–MTX solution at 700 nm in the pH value range from 5 to 6. Moreover, the Tyndall effect of the calixpyridinium–MTX solution disappeared under the acidic and alkaline conditions (Fig. 12). Both experimental results indicated that the optimal pH environment for the formation of the calixpyridinium–MTX supramolecular aggregates was weak acidic. It is in accordance with the living environment of cancer cell [40]. Therefore, it is quite important for the possible adjustment of the efficacy of MTX by the aggregation between calixpyridinium and MTX in the environment of cancer cell. The possible reason for the disassembly of the calixpyridinium–MTX aggregates under alkaline condition is the reduced positive charge of calixpyridinium from protonated to deprotonated state of the methylene bridges in calixpyridinium (Fig. S15a) [26]. It would lead to a weaker electrostatic interaction between calixpyridinium and negatively charged MTX. The possible reason for the disassembly of the calixpyridinium–MTX aggregates under acidic condition is the reduced negative charge of MTX from deprotonated to protonated state of the anions in MTX (Fig. S15b). It also would lead to a weaker electrostatic interaction between positively charged calixpyridinium and MTX. Neutral macrocyclic cyclodextrin can also bind with anionic organic molecules driven by hydrophobic and hydrogen bonding interactions between host and guest [41]. However, cyclodextrin could not bind with MTX (Fig. S16). It implied that the electrostatic and charge-transfer interactions between the cationic macrocyclic calixpyridinium and the anionic MTX were quite important for the formation of the calixpyridinium–MTX supramolecular amphiphilic aggregates.
Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.tetlet.2019.151357. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]
Conclusions The host–guest interaction between calixpyridinium and the anionic anticancer drug MTX was explored in water. Unexpectedly, the complexation of calixpyridinium with MTX leaded to the formation of an interesting anisotropic needle-like rather than an ordinary isotropic spherical supramolecular amphiphilic assembly. It is the second anionic guest to be discovered to form the nonspherical supramolecular assembly upon complexation with calixpyridinium. This discovery implies the possibility to construct various topological nanostructures based on the host–guest interactions between calixpyridinium and the anionic drugs in the future. The resulting calixpyridinium–drug assemblies with different morphologies may have the diverse potentials to adjust the efficacies of anionic drugs.
[18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30]
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
[31] [32] [33] [34] [35]
Acknowledgements
[36] [37]
We thank the National Natural Science Foundation of China (21402141, 21302140, and 21572160), the Natural Science Foundation of Tianjin City (18JCQNJC06700), the Foundation of STITP in Tianjin Normal University (201910065083), the Foundation of Development Program of Future Expert in Tianjin Normal University (WLQR201909), and the Program for Innovative Research Team in University of Tianjin (TD13-5074) for financial support.
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Please cite this article as: K. Wang, M. N. Wang, Q. Q. Wang et al., Needle-like supramolecular amphiphilic assembly constructed by the host–guest interaction between calixpyridinium and methotrexate disodium, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.151357
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Needle-like supramolecular amphiphilic assembly constructed by the host–guest interaction between calixpyridinium and methotrexate disodium Kui Wang ⇑, Mi-Ni Wang, Qi-Qi Wang, Yu-Xin Feng, Yue Wu, Si-Yang Xing ⇑, Bo-Lin Zhu ⇑, Ze-Hao Zhang Tianjin Key Laboratory of Structure and Performance for Functional Molecules, MOE Key Laboratory of Inorganic-Organic Hybrid Functional Material Chemistry, College of Chemistry, Tianjin Normal University, Binshuixi Road 393, Xiqing District, Tianjin 300387, China
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Article history: Received 30 September 2019 Revised 28 October 2019 Accepted 2 November 2019 Available online xxxx Keywords: Supramolecular assembly Host–guest systems Macrocycle Calixpyridinium
a b s t r a c t In this work, the host–guest interaction between calixpyridinium and the anionic anticancer drug methotrexate disodium was explored in water. Unexpectedly, an interesting anisotropic needle-like rather than an ordinary isotropic spherical supramolecular amphiphilic assembly was fabricated by the complexation of calixpyridinium with methotrexate disodium. It is the second anionic guest to be discovered to form the non-spherical supramolecular assembly upon complexation with calixpyridinium. This discovery implies the possibility to construct various topological nanostructures based on the host–guest interactions between calixpyridinium and the anionic drugs in the future. The resulting calixpyridinium– drug assemblies with different morphologies may have the diverse potentials to adjust the efficacies of anionic drugs. Ó 2019 Elsevier Ltd. All rights reserved.
Introduction Cancer is one of the diseases with highest morbidity and mortality in the world. According to the world health organization, one in 5 men and one in 6 women worldwide develop cancer during their lifetime, and one in 8 men and one in 11 women die from the disease [1]. Up to now, the etiology of malignant tumor has not been fully understood yet. Although the new therapies appear continuously, cancer has not been completely conquered. Chemotherapy is still one of the most effective antitumor therapies [2,3]. However, most chemotherapeutic agents have serious side effects. They cannot distinguish cancer cells from normal tissue. Therefore, chemotherapy is a double-edged sword and it causes great suffering to patients. Recently, the method of supramolecular inclusion by the macrocyclic hosts paves a smart way to reduce the side effects of drugs. Zhang et al. proposed a new concept of supramolecular chemotherapy, which aimed to reduce the toxicity of chemotherapeutic drugs to normal cells and improve their anti-cancer efficacy by combining the macrocyclic hosts and the anticancer drugs based on host–guest interactions [4]. Some macrocyclic hosts, such as cucurbit[7]uril and water-soluble pillar[6]arene, have been ⇑ Corresponding authors. E-mail addresses: [email protected] (K. Wang), [email protected] (S.-Y. Xing), [email protected] (B.-L. Zhu).
successfully applied in the supramolecular chemotherapy [5–9]. Besides anticancer drugs, the efficacies of other drugs have also been successfully adjusted by the method of supramolecular inclusion based on the macrocyclic cucurbiturils [10–14], cyclodextrins [15], pillararenes [16], and sulfonatocalixarenes [17–19]. It is noticeable, however, most of these frequently used macrocyclic hosts in this field are the suitable receptors for cationic and neutral drugs. Adjusting the efficacies of the anionic drugs by supramolecular strategy based on the inclusion of macrocyclic hosts via the host–guest interactions has been explored much less frequently. In fact, the anionic drugs are also quite widespread and important. Calixpyridinium, obtained by the oligomerization of 3-bromomethylpyridine, is a positively charged macrocyclic host and has excellent water-solubility [20]. In recent years more and more attentions have been paid in this macrocyclic host because it has exhibited good binding abilities with anionic guests in aqueous solution [20–24]. Moreover, polyanionic guests [25–28] and anionic gemini surfactant guests [29] have been found to form the higherorder assemblies rather than the simple complexes upon complexation with calixpyridinium. Although calixpyridinium has been proved to be a good receptor for anions in aqueous media [30], the host–guest interactions between calixpyridinium and the anionic drugs have been explored much less frequently. Recently, we reported a study on the host–guest interaction between calixpyridinium and the anionic anticancer drug Alimta. The isotropic spherical supramolecular amphiphilic assembly rather than the simple
https://doi.org/10.1016/j.tetlet.2019.151357 0040-4039/Ó 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: K. Wang, M. N. Wang, Q. Q. Wang et al., Needle-like supramolecular amphiphilic assembly constructed by the host–guest interaction between calixpyridinium and methotrexate disodium, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.151357
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Scheme 1. Schematic illustration of the needle-like supramolecular assembly constructed by the host–guest interaction between calixpyridinium and MTX.
Fig. 1. Dependence of the optical transmittance at 500 nm on the MTX concentration in the presence of 0.10 mM (a), 0.15 mM (b), and 0.20 mM (c) calixpyridinium.
complex was unexpectedly fabricated benefitting from the additional charge-transfer interactions besides the electrostatic interactions between calixpyridinium and Alimta [31]. Macrocyclic
host-based supramolecular amphiphilic assembly can be tailored to construct various topological nanostructures, and therefore fulfill multiple applications [32–38]. Inspired by this new discovery, we
Please cite this article as: K. Wang, M. N. Wang, Q. Q. Wang et al., Needle-like supramolecular amphiphilic assembly constructed by the host–guest interaction between calixpyridinium and methotrexate disodium, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.151357
K. Wang et al. / Tetrahedron Letters xxx (xxxx) xxx
tried to fabricate more topological nanostructures that were different from ordinary isotropic spheres based on the supramolecular amphiphilic assembly between calixpyridinium and the anionic drugs. Methotrexate disodium (MTX) is a folate antagonist and has been widely used in the treatment of various types of cancers including breast, leukemia, lymphoma, lung and osteosarcoma [39]. Herein, the host–guest interaction between calixpyridinium and MTX was explored. Unexpectedly, completely differing from the ordinary isotropic spherical supramolecular amphiphilic assembly constructed by the host–guest interaction between calixpyridinium and Alimta, an interesting anisotropic needle-like supramolecular assembly was fabricated (Scheme 1), although the structures of Alimta and MTX are very similar. It is the second anionic guest to be discovered to form the non-spherical supramolecular assembly upon complexation with calixpyridinium besides sodium alginate with low viscosity, which formed a lamellar structure by the host– guest interaction of calixpyridinium [25]. This discovery implies the possibility to construct various topological nanostructures based on the host–guest interactions between calixpyridinium and the anionic drugs in the future. The resulting calixpyridinium–drug assemblies with different morphologies may have the diverse potentials to adjust the efficacies of the anionic drugs. Results and discussion The calixpyridinium-complexation-induced critical aggregation concentration (CAC) of MTX was first determined by measuring the optical transmittance of the calixpyridinium solution in the presence of different concentrations of MTX (Fig. S1). As can be seen from Fig. 1, there was no obvious change in the optical
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transmittance of the calixpyridinium solution over 500 nm with the addition of a small amount of MTX. Further addition of MTX leaded to a dramatic decrease in the optical transmittance of the calixpyridinium solution over 500 nm accompanied by the appearance of turbidity because of the supramolecular amphiphilic assembly between calixpyridinium and MTX. The calixpyridinium-complexation-induced CAC of MTX could therefore be determined by observing the inflection point on the plot of the optical transmittance at 500 nm versus the concentrations of MTX: 120 lM at 0.10 mM calixpyridinium, 100 lM at 0.15 mM calixpyridinium, and 53 lM at 0.20 mM calixpyridinium. The calixpyridinium-complexation-induced CAC of MTX was further determined by measuring the electrical conductivity of the calixpyridinium solution in the presence of different concentrations of MTX. As can be seen from Fig. 2, the addition of a small amount of MTX leaded to a linear increase in the electrical conductivity of the calixpyridinium solution. Further addition of MTX leaded to a slower increase in the electrical conductivity of the calixpyridinium solution because of the formation of large calixpyridinium–MTX supramolecular amphiphilic assembly. The calixpyridinium-complexation-induced CAC of MTX could therefore be determined by observing the inflection point on the plot of the electrical conductivity versus the concentrations of MTX: 40 lM at 0.10 mM calixpyridinium, 70 lM at 0.15 mM calixpyridinium, and 37 lM at 0.20 mM calixpyridinium. The calixpyridinium-complexation-induced CAC values of MTX determined by optical transmittance and electrical conductivity were in the same order of magnitude. Next, the MTX-complexation-induced CAC of calixpyridinium was determined by measuring the optical transmittance of the
Fig. 2. Dependence of the electrical conductivity on the MTX concentration in the presence of 0.10 mM (a), 0.15 mM (b), and 0.20 mM (c) calixpyridinium in water.
Please cite this article as: K. Wang, M. N. Wang, Q. Q. Wang et al., Needle-like supramolecular amphiphilic assembly constructed by the host–guest interaction between calixpyridinium and methotrexate disodium, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.151357
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Fig. 3. Dependence of the optical transmittance at 500 nm on the calixpyridinium concentration in the presence of 0.07 mM (a), 0.10 mM (b), and 0.15 mM (c) MTX.
MTX solution in the presence of different concentrations of calixpyridinium (Fig. S2). As can be seen from Fig. 3, similarly, there was no obvious change in the optical transmittance of the MTX solution over 500 nm with the addition of a small amount of calixpyridinium. Further addition of calixpyridinium leaded to a dramatic decrease in the optical transmittance of the MTX solution over 500 nm accompanied by the appearance of turbidity because of the supramolecular amphiphilic assembly between calixpyridinium and MTX. The MTX-complexation-induced CAC of calixpyridinium could therefore be determined by observing the inflection point on the plot of the optical transmittance at 500 nm versus the concentrations of calixpyridinium: 29 lM at 0.07 mM MTX, 72 lM at 0.10 mM MTX, and 8.6 lM at 0.15 mM MTX. The MTX-complexation-induced CAC of calixpyridinium was also further determined by measuring the electrical conductivity of the MTX solution in the presence of different concentrations of calixpyridinium. As can be seen from Fig. 4, similarly, the addition of a small amount of calixpyridinium leaded to a linear increase in the electrical conductivity of the MTX solution. Further addition of calixpyridinium leaded to a slower increase in the electrical conductivity of the MTX solution because of the formation of calixpyridinium–MTX supramolecular amphiphilic assembly. The MTXcomplexation-induced CAC of calixpyridinium could therefore be determined by observing the inflection point on the plot of the electrical conductivity versus the concentrations of calixpyridinium: 98 lM at 0.07 mM MTX, 168 lM at 0.10 mM MTX, and 4.4 lM at 0.15 mM MTX. The MTX-complexation-induced CAC values of calixpyridinium determined by optical transmittance and electrical conductivity were also in the same order of magnitude. Although different concentrations of calixpyridinium and MTX can all mutually induce aggregation, it is necessary to determine
the optimal stoichiometry between calixpyridinium and MTX for constructing the calixpyridinium–MTX supramolecular amphiphilic aggregates via the continuous variation method by observing the dependence of the optical transmittance at 500 nm on the molar ratio of calixpyridinium (Fig. S3). As can be seen from Fig. 5, a minimum was determined in the Job’s plot for a 0.33 M ratio of calixpyridinium when the total concentration of calixpyridinium and MTX was kept constant at 0.20 mM. This indicated that the optimal stoichiometry between calixpyridinium and MTX for constructing the calixpyridinium–MTX supramolecular aggregates is 1:2. It was also a charge matching ratio between calixpyridinium and MTX. The CAC of the 1:2 calixpyridinium–MTX complex for constructing the supramolecular aggregates was further determined by measuring the optical transmittance of different concentrations of the 1:2 calixpyridinium–MTX solution (Fig. S4). As can be seen from Fig. 6, there was no obvious change in the optical transmittance over 500 nm with the addition of a small amount of the 1:2 calixpyridinium–MTX complex. Further addition of the 1:2 calixpyridinium–MTX complex leaded to a dramatic decrease in the optical transmittance over 500 nm accompanied by the appearance of turbidity because of the supramolecular amphiphilic assembly between calixpyridinium and MTX. The CAC of the 1:2 calixpyridinium–MTX complex for constructing the supramolecular aggregates could therefore be determined by observing the inflection point on the plot of the optical transmittance at 500 nm versus the concentrations of calixpyridinium: 42 lM calixpyridinium–84 lM MTX. Further studies on the calixpyridinium– MTX aggregates were focused on a concentration of 0.10 mM calixpyridinium–0.20 mM MTX. This concentration is far higher than its CAC to ensure the complete aggregation between calixpyridinium and MTX.
Please cite this article as: K. Wang, M. N. Wang, Q. Q. Wang et al., Needle-like supramolecular amphiphilic assembly constructed by the host–guest interaction between calixpyridinium and methotrexate disodium, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.151357
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Fig. 4. Dependence of the electrical conductivity on the calixpyridinium concentration in the presence of 0.07 mM (a), 0.10 mM (b), and 0.15 mM (c) MTX in water.
Fig. 5. Job’s plot for calixpyridinium and MTX in water. [Calixpyridinium] + [MTX] = 0.20 mM.
As can be seen from Fig. 7a, the calixpyridinium–MTX solution showed the obvious Tyndall effect because of the existence of abundant nanoparticles formed by the supramolecular amphiphilic assembly between calixpyridinium and MTX. However, no Tyndall effect was observed for free calixpyridinium and MTX solutions, proving that free calixpyridinium and MTX could not form aggregates under the same conditions. Furthermore, 1-methylpyridinium, the building subunit of calixpyridinium, could also not form supramolecular aggregates upon complexation with MTX, which has been proved by the Tyndall effect (Fig. 7a) and the
Fig. 6. Dependence of the optical transmittance at 500 nm on the calixpyridinium concentration in the calixpyridinium–MTX solution with a fixed 1:2 stoichiometry.
optical transmittance (Fig. 7b). This implied that the cyclic polycationic structure of calixpyridinium was a crucial factor for the supramolecular amphiphilic assembly between calixpyridinium and MTX. High-resolution transmission electron microscopy (TEM), scanning electron microscope (SEM) and dynamic light scattering (DLS) were then employed to determine the structure and size of the calixpyridinium–MTX supramolecular aggregates. Unexpectedly, completely differing from the ordinary spherical supramolecular aggregates formed by the complexation of calixpyridinium with Alimta [31], an interesting needle-like supramolecular amphiphilic assembly was constructed
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Fig. 7. (a) Photograph showing the Tyndall effect of 1-methylpyridinium chloride + MTX (I), free MTX (II), free calixpyridinium (III) and calixpyridinium + MTX (IV). (b) Optical transmittance of calixpyridinium, MTX, calixpyridinium + MTX, and 1-methylpyridinium chloride + MTX in water. (c) High-resolution TEM image of the calixpyridinium–MTX assemblies. (d) SEM image of the calixpyridinium–MTX assemblies. (e) DLS data of the calixpyridinium–MTX assemblies. [Calixpyridinium] = 0.10 mM, [MTX] = 0.20 mM, and [1-methylpyridinium chloride] = 0.40 mM.
(Figs. 7c, d and S5), although the structures of Alimta and MTX are very similar. The average diameter of the supramolecular amphiphilic aggregates in solution measured by DLS was 532.7 nm (Fig. 7e). The binding mode of calixpyridinium with MTX in the calixpyridinium–MTX supramolecular aggregates was further deduced by analyzing complexation-induced 1H chemical shift changes (Dd) of calixpyridinium and MTX. As shown in Fig. 8, an obvious upfield shift was found for the Hb, Hc, Hd, and He proton signal of calixpyridinium upon complexation with MTX. Meanwhile, an obvious downfield shift was found for the Ha proton signal of calixpyridinium. This indicated undoubtedly that MTX was bound with calixpyridinium. Compared with the binding structure between
calixpyridinium and Alimta in the calixpyridinium–Alimta supramolecular aggregates, MTX was bound much closer to the cavity of calixpyridinium because the Ha proton signal of calixpyridinium almost did not shift upon complexation with Alimta [31]. It may be a key factor for the different morphologies formed by the complexation of calixpyridinium with MTX and Alimta as shown in Scheme 1. On the other hand, as shown in Fig. 8, an obvious upfield shift was found for the H1–H4 proton signal of MTX upon complexation with calixpyridinium while the H6 proton signal of MTX almost did not shift, which implied that the nitrogen heterocyclic ring and benzene ring were two possible charge-transfer binding sites of MTX with calixpyridinium. The color of the MTX solution became darker upon complexation with calixpyridinium
Please cite this article as: K. Wang, M. N. Wang, Q. Q. Wang et al., Needle-like supramolecular amphiphilic assembly constructed by the host–guest interaction between calixpyridinium and methotrexate disodium, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.151357
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Fig. 8. 1H NMR spectra of calixpyridinium (bottom), MTX (top), and calixpyridinium–MTX complex (middle) in D2O solutions. Inset: the color of the D2O solution of calixpyridinium (bottom), MTX (top), and calixpyridinium–MTX complex (middle). [Calixpyridinium] = 5 mM, and [MTX] = 10 mM.
Fig. 9. (a) Dependence of the optical transmittance at 500 nm of the calixpyridinium–MTX assembly on time within 18 h at room temperature in water. (b) Optical transmittance of the calixpyridinium–MTX assembly before and after centrifugation for one minute at 1000 r/min in aqueous solution. Inset: the Tyndall effect of the calixpyridinium–MTX solution before (I) and after centrifugation for one minute (II). [Calixpyridinium] = 0.10 mM, and [MTX] = 0.20 mM.
(Fig. 8), which further proved the existence of a charge-transfer interaction between calixpyridinium and MTX. Meanwhile an obvious downfield shift was found for the H7 proton signal of MTX while the H5 and H8 proton signal of MTX almost did not shift, which implied that the negatively charged carboxylate connected to H7 was the third possible binding site of MTX with calixpyridinium accompanied by electrostatic interactions. The binding ability of calixpyridinium with MTX was further estimated by the competitive binding of MTX with calixpyridinium. As can be seen from Fig. S6a, the addition of 2 equiv of MTX in the calixpyridinium–1,3,6,8-pyrenetetrasulfonic acid tetrasodium salt (PyTS) solution could not affect its optical transmittance, suggesting that MTX could not competitively bind with the calixpyridinium in calixpyridinium–PyTS complex. However, as can be seen from Fig. S6b, the addition of 2 equiv of MTX in the calixpyridinium–glyphosate solution leaded to a decrease in
its optical transmittance, suggesting that MTX could competitively bind with the calixpyridinium in calixpyridinium–glyphosate complex to form calixpyridinium–MTX aggregates. Both of the two competitive binding experimental results indicate that the binding ability of calixpyridinium with MTX is moderate because the binding ability of calixpyridinium with PyTS and glyphosate is strong (The binding constant is in the order of magnitude of 106 M 1) [23] and weak (The binding constant is in the order of magnitude of 102 M 1) [24], respectively. In order to explore the stability of the calixpyridinium–MTX supramolecular aggregates, their tolerance to time, centrifugation, temperature and even salt was studied. As can be seen from Figs. S7 and 9a, there was no obvious change in the optical transmittance of the calixpyridinium–MTX solution over at least 18 h at room temperature. The optical transmittance and the Tyndall effect of the calixpyridinium–MTX solution could also not be
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Fig. 10. (a) Dependence of the optical transmittance at 500 nm of the calixpyridinium–MTX assembly on the concentration of NaCl. Inset: the Tyndall effect of the calixpyridinium–MTX solution in the absence (I) and presence (II) of 0.54 mM NaCl. (b) Dependence of the optical transmittance at 500 nm of the calixpyridinium–MTX assembly on time within 6 h in the presence of 0.54 mM NaCl. Inset: the Tyndall effect of the calixpyridinium–MTX assembly immediately after the preparation (I) and 6 h after the preparation (II) in the presence of 0.54 mM NaCl. [Calixpyridinium] = 0.10 mM, and [MTX] = 0.20 mM.
Fig. 11. Dependence of the optical transmittance at 500 nm on the MTX concentration in the presence of 0.10 mM calixpyridinium in saline solution.
disturbed after centrifugation for one minute at 1000 r/min (Fig. 9b). Both experimental results indicated that the calixpyridinium–MTX supramolecular aggregates had sufficient stability at room temperature. As can be seen from Fig. S8, there was also no obvious change in the optical transmittance of the calixpyridinium–MTX solution with temperature ascending from 20 to 40 °C, implying that the calixpyridinium–MTX supramolecular aggregates even had sufficient stability to the temperature of a cancer patient with fever. The tolerance of the calixpyridinium– MTX supramolecular aggregates to NaCl was further studied for their possible biomedical applications in a complex biological environment. As can be seen from Figs. S9 and 10a, there was no obvious change in the optical transmittance of the calixpyridinium– MTX solution in the presence of NaCl from 15 lM to 5.34 mM. The Tyndall effect of the calixpyridinium–MTX solution could also not be disturbed in the presence of NaCl (Fig. 10a). Moreover, the optical transmittance and the Tyndall effect of the calixpyridinium–MTX solution in the presence of NaCl could even not be disturbed over 6 h (Figs. S10 and 10b). The calixpyridinium-complexation-induced CAC of MTX was further measured in saline solution (Fig. S11). As can be seen from Fig. 11, the calixpyridinium-complexation-induced CAC of MTX in saline solution was 62 lM at 0.10 mM calixpyridinium, which was in the same order of magnitude as that in pure water. Moreover, the calixpyridinium–MTX supramolecular aggregates in saline solution also
Fig. 12. Dependence of the optical transmittance at 700 nm on the pH value of the calixpyridinium–MTX aqueous solution. Inset: the left photograph showing the Tyndall effect of the calixpyridinium–MTX solution at pH = 6 and pH = 2 at room temperature in water. The right photograph showing the Tyndall effect of the calixpyridinium–MTX solution at pH = 6 and pH = 9 at room temperature in water. [Calixpyridinium] = 0.10 mM, and [MTX] = 0.20 mM.
had sufficient stability (Fig. S12). All of these experimental results in the presence of NaCl suggested that these aggregates were possibly suitable for the biomedical applications. The heat effect for the formation of calixpyridinium–MTX supramolecular amphiphilic aggregates was studied by observing the optical transmittance of the calixpyridinium–MTX solution with a further increase of the temperature. As can be seen from Fig. S13, there was a little increase in the optical transmittance of the calixpyridinium–MTX solution with the temperature ascending from 20 to 60 °C, accompanied by the obvious reduction of the Tyndall effect. This implied that the formation of the calixpyridinium–MTX supramolecular aggregates was exothermic because increasing temperature leaded to the disassembly of the aggregates. The optimal pH environment for the formation of the calixpyridinium–MTX supramolecular aggregates was also studied by observing the optical transmittance of the calixpyridinium–MTX solution at various pH values because both calixpyridinium and MTX could be affected by pH (Fig. S14). As can be seen from Fig. 12, there was an obvious decrease in the optical transmittance
Please cite this article as: K. Wang, M. N. Wang, Q. Q. Wang et al., Needle-like supramolecular amphiphilic assembly constructed by the host–guest interaction between calixpyridinium and methotrexate disodium, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.151357
K. Wang et al. / Tetrahedron Letters xxx (xxxx) xxx
of the calixpyridinium–MTX solution at 700 nm in the pH value range from 5 to 6. Moreover, the Tyndall effect of the calixpyridinium–MTX solution disappeared under the acidic and alkaline conditions (Fig. 12). Both experimental results indicated that the optimal pH environment for the formation of the calixpyridinium–MTX supramolecular aggregates was weak acidic. It is in accordance with the living environment of cancer cell [40]. Therefore, it is quite important for the possible adjustment of the efficacy of MTX by the aggregation between calixpyridinium and MTX in the environment of cancer cell. The possible reason for the disassembly of the calixpyridinium–MTX aggregates under alkaline condition is the reduced positive charge of calixpyridinium from protonated to deprotonated state of the methylene bridges in calixpyridinium (Fig. S15a) [26]. It would lead to a weaker electrostatic interaction between calixpyridinium and negatively charged MTX. The possible reason for the disassembly of the calixpyridinium–MTX aggregates under acidic condition is the reduced negative charge of MTX from deprotonated to protonated state of the anions in MTX (Fig. S15b). It also would lead to a weaker electrostatic interaction between positively charged calixpyridinium and MTX. Neutral macrocyclic cyclodextrin can also bind with anionic organic molecules driven by hydrophobic and hydrogen bonding interactions between host and guest [41]. However, cyclodextrin could not bind with MTX (Fig. S16). It implied that the electrostatic and charge-transfer interactions between the cationic macrocyclic calixpyridinium and the anionic MTX were quite important for the formation of the calixpyridinium–MTX supramolecular amphiphilic aggregates.
Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.tetlet.2019.151357. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]
Conclusions The host–guest interaction between calixpyridinium and the anionic anticancer drug MTX was explored in water. Unexpectedly, the complexation of calixpyridinium with MTX leaded to the formation of an interesting anisotropic needle-like rather than an ordinary isotropic spherical supramolecular amphiphilic assembly. It is the second anionic guest to be discovered to form the nonspherical supramolecular assembly upon complexation with calixpyridinium. This discovery implies the possibility to construct various topological nanostructures based on the host–guest interactions between calixpyridinium and the anionic drugs in the future. The resulting calixpyridinium–drug assemblies with different morphologies may have the diverse potentials to adjust the efficacies of anionic drugs.
[18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30]
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
[31] [32] [33] [34] [35]
Acknowledgements
[36] [37]
We thank the National Natural Science Foundation of China (21402141, 21302140, and 21572160), the Natural Science Foundation of Tianjin City (18JCQNJC06700), the Foundation of STITP in Tianjin Normal University (201910065083), the Foundation of Development Program of Future Expert in Tianjin Normal University (WLQR201909), and the Program for Innovative Research Team in University of Tianjin (TD13-5074) for financial support.
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Please cite this article as: K. Wang, M. N. Wang, Q. Q. Wang et al., Needle-like supramolecular amphiphilic assembly constructed by the host–guest interaction between calixpyridinium and methotrexate disodium, Tetrahedron Letters, https://doi.org/10.1016/j.tetlet.2019.151357